What color is the emergency meeting/assembly circle painted on the floor in case of fires is?

I don't think that there's any universal regulations as to what colour it should be. I would be tempted to make it a red flame inside a circle. One company that I worked for had these numbered signs just inside the stair well for each floor. The first person to exit from each floor was to grab that sign and hold it up in the parking lot so that people would congregate by floor number. The unofficial rule was that should there be a real fire, the bar across the street would be where people would be found.